1. Field of the Invention
The present invention relates in general to a discharge wire for use in an electrostatic precipitator used for collecting pollutant particles contained in an exhaust gas flow. In particular, the discharge wire is a chain having a plurality of needle-like members provided thereon.
2. Description of Prior Art
To protect the environment, factory facilities which produce exhaust gases containing a large amount of smoke and dust are generally opposed by environmentalists. Therefore an electrostatic precipitator (ESP) is installed at the exhaust gas outlet for collecting the pollutant particles contained in the exhaust gas before the exhaust gas is released into the atmosphere.
Referring to FIG. there is shown a schematic illustration of an electrostatic precipitator 10. The electrostatic precipitator 10 comprises a pair of collecting plates 12 arranged in parallel to each other and a discharge wire 20 disposed between the pair of collecting plates 11, 12. In the illustrated exemplary electrostatic precipitator, three such arrangements are disposed along the exhaust gas passage.
The conventional structure of the discharge wires 20 is shown in FIG. 2, which is an angle bar having a plurality of pikes 21 formed at the edges thereof.
The conventional discharge wires 20 are connected to the negative electrode 31 of a DC potential 30 and the collecting plates 11, 12 are connected to the positive electrode 32 of the same such that an electric potential is directed from the collecting plates 11, 12 to the conventional discharge wires 20. The collecting plates 11, 12 are further connected to the ground. The electric field established between the collecting plates 11, 12 and the discharge wire 20 is shown in FIG. 3.
The electric potential thus applied should be large enough to cause corona currents at the tips of the pikes 21. The corona currents are basically beams of electrons discharged at high velocities from the tips of the pikes 21 to the collecting plates 11, 12.
As the rapidly moving electrons which have been discharged from the discharge wire 20 encounter air molecules, the air molecules are ionized, thereby creating positively charged air molecules and more free drifting electrons. The positively charged air molecules are attracted by the electric field and move toward the discharge wire 20. At the same time, the electrons are forced by the electric field to move toward the collecting plates 11, 12.
When the pollutant particles pass through the space between the collecting plates 11, 12, the corona current imparts negative charges to the pollutant particles. These negatively charged particles are then attracted to the collecting plates 11, 12 which are positively charged. The collected pollutant particles will accumulate to a thick layer of agglomeration. By applying mechanical rapping to the collecting plates, the thick layer of agglomeration can be removed to be collected by the collection buckets 40 which are placed below the collecting plates 11, 12.
Since most of the pollutant particles contained in the exhaust gas have been collected by the collecting plates 11, 12, what exits from the electrostatic precipitator 10 is substantially a gas flow without smoke or dust.
The above described electrostatic precipitator which utilizes the conventionally structured discharge wire has a high particle-collecting efficiency (more than 99%) and is also easy to maintain. However, since the electrostatic precipitator requires a high electric potential (about 30-40 Kilovolt) to generate the corona current, the costs for electric energy are normally quite high.